In one word, ENTROPY is "Thermal-space" or Thermal-disorder displacement space, not any other disorder.

Thermal-energy, Eth=T*S,  as disordered thermal-motion, is "spread" over its own thermal-space (Entropy S), like mechanical-energy, Emech=P*V, is "spread" over its mechanical-space (Volume V).

The mass-energy of material systems (or energy for short) is distributed (or displaced) within the systems’ energy space or displacement space, or displacement or extensity for short (e.g., Volume as Mechanical-energy space, or Entropy as Thermal-energy space, etc.), with energy density, i.e., energy per unit of its displacement space or energy intensity or energy force, or force for short (e.g., Pressure or Temperature, etc.). The displacement-space is the energy extensive property, and by definition, "energy-space" is conjugate with its "energy-force"; see [Kostic 2023, Table 1].

 Entropy Statistical Limitations * Entropy & Disorder * Entropy Misconceptions * Comments to Leff's Key Points (*) * Snapshot * PDF of this page


If an educated person has to be aware of the literary work of Shakespeare, then that person should also be aware of the Entropy concept.”

Entropy SchPed*Entropy is a dim * Grand LawEnergy2nd LawEntropy

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Abstract: Entropy is the most used and often abused concept in science, but also in philosophy and society. Further confusions are produced by some attempts to generalize entropy with similar but not the same concepts in other disciplines. The physical meaning of phenomenological, thermodynamic entropy is reasoned and elaborated by generalizing Clausius definition with inclusion of generated heat, since it is irrelevant if entropy is changed due to reversible heat transfer or irreversible heat generation.Click for Full Abstract


What is the underlying nature of “entropy” and why does it always increase? Why is entropy so intriguing and mysterious, unique and universal, as if it is a miraculous property of natural, material systems? How does it encompass and quantify all processes at all natural space and time scales, governed by the Second Law of Thermodynamics? And many other elusive and debatable issues, as if entropy is among the deepest unresolved mysteries in nature, defying our common sense. 

The intention of this treatise is not a review of vast entropy literature, but presentation of this author’s long-contemplated reflections on physical meaning of entropy, and to put certain physical and philosophical concepts in perspective. Only two seminal references and two related publications by the author, in addition to three popular references to illustrate certain misconceptions, are cited. 

Entropy Is Not a space disorder, nor form, nor  functional disorder. Entropy IS thermal displacement ("thermal-motion space" i.e., thermal disorder space). No thermal motion, no entropy! Expanding entropy to any type of disorder or information is a source of many misconceptions.

Nothing occurs locally, nor globally in the universe, without mass-energy exchange/conversion and entropy production. 

It is crystal-clear (to me) that all confusions related to the far-reaching fundamental Laws of Thermodynamics, and especially the Second Law (Abstract & FULL paper), are due to the lack of their genuine and subtle comprehension. > Sadi Carnot's Reflections <*> Clausius Theory of Heat <

 Elusive Nature of Entropy, Nature of Thermal and Mechanical Energy Transfer and Reflections on the Caloric Theory and Thermal Energy. * Feynman's Lecture

"Entropy is associated with stored-heat within a material system, i.e. its thermal energy. It is an integral measure of thermal energy per absolute temperature of a system (transferred as heat into and generated heat within, due to work potential dissipation to thermal heat). As heat is generated due to dissipation of any work potential to heat, the entropy is irreversibly produced. However, if heat is converted to work (like in heat engines), the thermal energy is reduced while transferred to a lower-temperature thermal reservoir, however, the entropy (as ratio of thermal heat to absolute temperature) will not be reduced but conserved in ideal, reversible processes (Qrev/T=const, Carnot Ratio Equality), or even the entropy will be produced (generated) in real (irreversible) processes for the amount of dissipated work-potential to stored heat (or thermal energy) per absolute temperature, regardless that the thermal energy is reduced (converted to work). Therefore, the entropy is always produced, locally and thus integrally or globally, and there is no way to destroy entropy, since it will be against the forced energy transfer from higher to lower potential [Kostic 2011 & 2014]."

PPS: We are aware that the thermal phenomena are elusive and coupled with other energy forms. 

I am working to decouple thermal, from other internal forms of energies, where the "caloric heat transfer processes" (only heating/cooling with full dissipation of work potential) and "reversible heat transfer" (with extraction of full Carnot work potential) are two extreme cases (the former fully dissipates work-potential, while the latter fully extracts-and-utilize it). A reasonable physical intuition has an advantage over "blind" analytics. For example, intuitively the change of Exergy should not depend on value of reference dead state (Po,To), even though the Exergy does, and analytics may misguide the physicality. For example:

Exergy of heat Q1 at temperature T1 is Ex1=Q1(1-To/T1) and for state 2 would be Ex2=Q2(1-To/T2), so:

      Ex1-Ex2=Q1(1-To/T1) - Q2(1-To/T2), as if it is a function of To.

However, for Exergy, i.e., the reversible work potential, the Q2/T2=Q1/T1, the relevant quantities are correlated, so the above is reduced to:

      Ex1-Ex2=Q1(1-To/T1) - (Q1T2/T1)(1-To/T2)=(Q1/T1)(T1-T2), thus NOT function of To!

The similar applies in general where internal energy U is used, since relevant U2 is correlated to U1 etc...  *Irreversible-Reversible Equilibrium

This is Prof. Kostic's Web site being transitioned from the original or Legacy Web(*) - sorry for broken links referring to it!